Flexible electric conductor



Jan. 19, 1943. J. HoEKsTRA ET AL 2,308,975

FLEXIBLE ELECTRIC CONDUCTOR Filed June 13, 1940 (b/vouc 7"/ ws coms AL ,06573975 me T/F/c/Au nur Patented Jan. 19, 1943 FLEXIBLE `ELECTRIC CONDUCTOR Johannes Hoekstra, and Joseph `Eugene Hubert Rieter,v Eindhoven, Netherlands; vested in the Alien Property Custodian l Application June 13, z1940, Serial No. 340,373

` In the Netherlands May 27, 1939 f claims. (ci. 174-123)- Our invention relates to flexible electric conductors having a thin coherent layer of insulating material.

It has been proposed to make such layers of various materia-ls and combinations thereof, butv we have found that materials previously used for this purpose are not entirely satisfactory from both the electrical and mechanical standpoints. Although many materials, such as rubber and acetyl cellulose are satisfactory mechanically, they are not entirely satisfactory electrically. More particularly, if wires provided with a thin layer of such material are subjected to a humid atmosphere, they do not retain a high insulation resistance, for example, a resistance of about 1010 ohms per meter of wire at a relative humidity of about 94%. On the other hand layers of chlorinated rubber are satisfactory from an electrical standpoint and their use makes it possible to secure low dielectric loss in a humid atmosphere, but such layers are too brittle if a softening agent is not used. If the usual softening agents are employed and are used in the usual manner, the chlorinated rubber, in particular at higher temperatures, comes too soft and the layers are capacity relatively to any metal parts along which the conductor may pass.

A further object is to produce an insulated conductor which is relatively ncombustible and is very resistant to the effect of humidity.

A further object is to provide a wire which is 1 especially adapted for use in carrier wave telephony, for example as connection wire in telephone exchange switchboards.

Further objects and advantages of our invention will appear as the description progresses.

In accordance with the present invention We obtain satisfactory results with insulating layers of chlorinated mixtures by using certain types of softening agents and using definite quantities of these agents. More particularly, we use an insulating layer consisting of a mixture of chlorinated rubber and a highly water-resistant softening agent, such as tricresylphosphate, in the amount of from about to 60% by Weight of the quantity of chlorinated rubber. Furthermore, we provide the insulated conductor with a top layer or coating of an insulating material which retains good mechanical properties at both high and lou/'temperatures This insulating top layer comprises a cellulose lacquer binder usually employed for insulating purposes containing a cellulose ether, such as ethylcellulose and benzylcellulose, or cellulose ester', such as cellulose acetate and cellulose aceto propionate, together with softening agents, such as tricresylphosphate, triphenylphosphate and tributylphosphate.' The insulation layers obtained `=in the above manner have excellent electrical properties and also excellent mechanical properties, particularly a high degreeof elasticity and'hardness even at relatively high and low temperatures. l

In order that the invention maybe clearly understood and readily carried into effect we shall describe the same in more detail with reference to the accompanying drawing in which the single figure is a sectionized view ony an enlarged scale of an insulated conductor according to the invention.: f-

The insulated conductor shown in the drawing comprises -a core I of conductive material, such as copper, provided with a tin coating and with an insulating covering 2 of an acetate artificial silk adapted for electrical purposes.A vThe covering 2 comprises four layers formed by winding the silk four times, alternatively in opposite directions. If desired, the outer layer of the covering 2 may be colored, or colored natural silk may be used to Wind this layer. The covering layer 2 serves to keep the dielectric constant at the surface of core l at allow value, thus reducing the capacity of the insulated conductor relatively to any metal parts along which it may pass.

Surrounding the covering 2 is an insulating layer 3 which is formed by applying thereto a. mixture of chlorinated rubber and a Water-resistant softening agent, the quantity of the softening agent being between about 35% to 60% by weight of the chlorinated rubber. As suitable softening agents we might mention tricresylphosphate and tributylphosphate. Particularly good results are obtained by using a mixture of 33% by weight of tricresylphosphate and 67% by weight of chlori-` nated rubber of high viscosity. This mixture may be applied by passing the covered core through the mixture same and then through a nipple to remove the excess mixture. We may also coat the core several times with the mixture which may be dissolved in a suitable solvent such as benzene or acetone to form a multi-layer coating. This coating is then dried by subjecting the conductor to either a stepwise or continuously increasing temperature. .We prefer to terminate the drying before all the solvent has been removed, because a small amount of residue solvent, not exceeding 7% by Weight, favorably in*- iluences the elasticity of the chlorinated rubber layer and this increased elasticity is especially advantageous when making connections with the wire. After considerable time the remaining solvent will, of course, evaporate, but this is not a disadvantage.

Surrounding layer 3 is an insulating top coating 4 of lacquer consisting, for example of about 57% by weight of acetyl cellulose, about 13% by weight of triphenylphosphate and about 30% by weight of tributylphosphate. It should be noted that special precautions are unnecessary in removing the solvent from this lacquer layer. In practice we prefer to dry the two layers 3 and 4 at the same time.

The conductors according to the invention have particularly advantageous electrical and mechanical properties, and at the same time are relatively incombustible due to the presence of chlorinated rubber mixtures` conductors particularly advantageous for use in cases where conductors are present in large quantities and there is thus great danger of fire, such as in ships and in telephone exchange oflices. The avoidance of this risk is of particular importance for telephone mounting and crossconnection wire, because wire for this purpose is designed to obtain a small electric capacity between two adjacent conductors, and it has been the practice to cover the same with an insulating organic fibrous layer of considerable thickness, which, however, materially increases the danger of fire.

In the specific example of the invention described above, the degree of incombustibility is also sufficient in practice for the purposes referred to.

Although we have described our invention with reference to specific examples and applications, we do not desire to be limited thereto because obvious modifications will present themselves to one skilled in the art.

What we claim is:

l. A flexible electrical conductor comprising a core of conductive material, an insulating coating surrounding said core and comprising chlorinated rubber and a water-resistant softening agent, the quantity and composition of the softening agent being such as to make the coating elastic and the quantity lying between 35% and 60% by weight of the quantity of chlorinated rubber, and a coating upon said first coating and This makes the containing a softening agent and a substance of the group consisting of cellulose ethers and cellulose esters.

2. A flexible electrical conductor comprising a core of conductive material, an insulating coating surrounding said core and comprising chlorinated rubber and tricresylphosphate, the quantity of the softening agent being between 35% and 60% by weight of the quantity of chlorinated rubber, and a coating upon said first coating and comprising a softening agent and a substance selected from the group consisting of cellulose ethers and cellulose esters.

3. A flexible electrical conductor comprising a core of conductive material, an insulating coating surrounding said core and comprising chlorinated rubber, a water-resistant softening agent and a solvent, the quantity and composition of the softening agent being such as to make the coating elastic and the quantity lying between 35% and 60% by vweight of the quantity of chlorinated rubber and the quantity of the solvent not exceeding '7% by weight of the quantitv of chlorinated rubber and softening agent, and a coating on said first coating and comprising a softening agent and a substance selected i'rom the group consisting of cellulose others and cellulose esters.

4. A flexible electrical conductor comprising a core of conductive material, a layer of organic brous material surrounding said core, an insulating coating on said layer and comprising chlorinated rubber and a water-resistant softening agent, thc quantity and composition of the softening agent being such as to msi-rc the coating elastic and the quantity lying between 35% and 60% by Weight of the quantity of chlorinated rubber, and a coating on said first coating and comprising a softening agent and a substance selected from the group consisting of cellulose ethers and cellulose esters.

5. A flexible electrical conductor comprising a core of copper with a tin coating, a layer of acetate artificial silk, an insulating coating on said layer consisting of about 67% by weight of chlorinated rubber and 33% by weight of tricresylphosphate, and a coating on said latter coating consisting of about 57% by weight of acetyl cellulose, 13%I by Weight of triphenylphosphate and 307c by weight of tributylphosphate.

JOHANNES HOEKSTrtA. JOSEPH EUGENE HUBERT RIETER. 

